Steel pipe for reinforcing ground, method of reinforcing ground using the same, and method of reinforcing structure

ABSTRACT

A steel pipe ground reinforcement of the present invention is driven into a ground and injects a grouting material into the ground. The steel pipe ground reinforcement includes: a recess portion and a smooth portion that are arranged on an outer peripheral surface thereof; and a plurality of through-holes that are arranged in the recess portion or the smooth portion that communicates between the inside and outside of the steel pipe ground reinforcement.

TECHNICAL FIELD

The present invention relates to a steel pipe ground reinforcementsuitable for use in a forepoling method in a tunnel construction and thelike, and in a method of reinforcing a excavation wall surface. Thepresent invention also relates to a method of reinforcing the groundusing the same and a method of reinforcing a structure such as aconcrete foundation using the same.

Priority is claimed on Japanese Patent Application No. 2008-009570,filed on Jan. 18, 2008, the contents of which are incorporated herein byreference.

BACKGROUND ART

For example, in a tunnel construction in the soft natural ground, aforepoling method of burying steel pipes is often adopted to reinforcethe natural ground. In this method, drilling is performed with a steelpipe being fitted onto a drilling rod whose forward end portion isattached with a bit. Then, after a hole with a predetermined depth isdrilled, the drilling rod is pulled out with the steel pipe left whereit is. Subsequently, a grouting material such as mortar is injected intothe steel pipe. A number of through-holes communicating between theinside and outside of the steel pipe are bored in a body of the steelpipe. The injected grouting material permeates into the natural groundthrough the through-holes, and then becomes solidified. As a result, thesoft natural ground is reinforced. As for the forepoling method, amultitude of patent applications have been filed (for example, seeJapanese Unexamined Patent Application, First Publication No.2000-204870 and No. 2001-020657).

The steel pipes used in the aforementioned forepoling method are buriedin the natural ground. Therefore, steel pipes with a material havinghigh strength at comparatively low cost are used. In injecting thegrouting material, it is required for the grouting material flowing outthrough the through-holes to sufficiently permeate into the naturalground and also to be densely filled in the gap between the naturalground and the steel pipe. Furthermore, for the buried steel pipe to besecurely fixed, it is desirable that the steel pipe and the layer of thegrouting material around the outer periphery of the steel pipe besecurely integrated.

However, a conventional steel pipe has its outer surface formed as asmooth surface, providing no hooking between itself and the layer of thegrouting material outside it. Therefore, it is not correct to say thatboth are secured with each other. As an improvement on this, there is amethod of subjecting an outer surface of a steel pipe to a sandblasttreatment or the like to make the surface rough. This method offers aclose contact effect in its own way. However, in terms of securelyfixing the steel pipe in the natural ground, it leaves something to bedesired.

Furthermore, Japanese Unexamined Patent Application, First PublicationNo. 2006-022501 (JPA 2006-022501) discloses a steel pipe groundreinforcement in which a protruded spiral strip is formed on its outerperiphery and a plurality of through-holes, which communicates betweenthe inside and outside of the steel pipe for allowing a groutingmaterial to flow out of the steel pipe, are provided in a space betweenthe protruded spiral strip.

However, the steel pipe disclosed in the above JPA 2006-022501 has aprotruded portion on its outer periphery. The protruded portionfunctions as an obstacle when the steel pipe is driven. In addition, theprotruded portion functions as an obstacle when earth and sand areexhausted from the outer surface side of the steel pipe. This preventsthe protruded portion from being formed in a large shape, resulting indifficulty to secure sufficient close contact. Furthermore, to provide aprotruded portion on the outer periphery of a steel pipe, an additionalstep of providing a protruded portion is required after the manufactureof the steel pipe. This leads to a problem of waning productivity andhigher cost.

The present invention is for solving the above problems, and has anobject to provide a steel pipe ground reinforcement that, withoutincreased manufacturing cost, offers low resistance when buried in theground and causes itself and its surroundings to be securely in closecontact with each other when a grouting material is poured. The presentinvention has a further object to provide a method of reinforcing theground using the steel pipe ground reinforcement and a method ofreinforcing a structure.

DISCLOSURE OF INVENTION

To solve the above problems and achieve such objects, the presentinvention adopts the following.

(1) A steel pipe ground reinforcement of the present invention is driveninto a ground and injects a grouting material into the ground. The steelpipe includes: a recess portion and a smooth portion that are arrangedon an outer peripheral surface thereof; and a plurality of through-holesthat are arranged in the recess portion or the smooth portion thatcommunicates between the inside and outside of the steel pipe groundreinforcement.

(2) The recess portion may have a cross-sectional shape with a depth ofthe recess portion of 0.005 D to 0.2 D and a width of the recess portionof 0.015 D to 2D where D is an outer diameter of the steel pipe, thatthe recess portion have a triangular shape in cross-section, and thatB/H=3 to 20 where B is the width of the recess portion and H is thedepth of the recess portion.

(3) The recess portion may have a cross-sectional shape with a depth ofthe recess portion of 0.005 D to 0.2 D and a width of the recess portionof 0.015 D to 2D where D is an outer diameter of the steel pipe, thatthe recess portion have a rectangular shape in cross-section, and thatB/H=4 to 20 where B is the width of the recess portion and H is thedepth of the recess portion.

(4) The recess portion may have a cross-sectional shape with a depth ofthe recess portion of 0.005 D to 0.2 D and a width of the recess portionof 0.015 D to 2D where D is an outer diameter of the steel pipe, thatthe recess portion have a semicircular or trapezoidal shape incross-section, and that B/H=3 to 20 where B is the width of the recessportion and H is the depth of the recess portion.

(5) A plurality of the recess portions may be provided on a sameperiphery of the steel pipe.

(6) A plurality of the recess portions may be provided in acircumferential direction of the steel pipe, and that at least therecess portions that face each other be provided so as to avoid being ona same periphery of the steel pipe.

(7) A plurality of the recess portions may be provided diagonally withrespect to an axis of the steel pipe.

(8) A plurality of the recess portions may be provided in parallel withrespect to an axis of the steel pipe.

(9) A plurality of the recess portions may be provided in a circularshape when seen from front.

(10) Plating or resin coating may be provided on the surface of thesteel pipe.

(11) A method of reinforcing the ground of the present inventionincludes: when reinforcing a ground, driving the steel pipe groundreinforcement according to the above (1) while drilling the ground; andafter driving of the steel pipe ground reinforcement, injecting agrouting material into an inside of the steel pipe ground reinforcementto thereby inject the grouting material into an outside of the steelpipe ground reinforcement through the plurality of through-holes.

(12) A minimum inner diameter of the steel pipe ground reinforcement maybe larger than an outer diameter of an inner bit that is used when theground is drilled.

(13) A maximum outer diameter of the steel pipe ground reinforcement maybe smaller than an outer diameter of an outer bit that is used when theground is drilled.

(14) A method of reinforcing a structure of the present inventionincluding concrete includes: when reinforcing a structure, driving thesteel pipe ground reinforcement according to claim 1 while drilling thestructure; and after driving of the steel pipe ground reinforcement,injecting a grouting material into an inside of the steel pipe groundreinforcement to thereby inject the grouting material into an outside ofthe steel pipe ground reinforcement through the plurality ofthrough-holes.

ADVANTAGEOUS EFFECTS OF INVENTION

The steel pipe ground reinforcement according to the above (1) has arecess portion formed in an outer peripheral surface of a steel pipe.Therefore, when buried in the ground, the recess portion will notfunction as a resistance (an obstacle). Furthermore, when poured aroundthe outer peripheral surface of the steel pipe, a grouting material isfilled also in the recess portion, improving close contact between thesteel pipe and the ground. As a result, it is possible to reduce thenumber of the steel pipes to be buried at the time of construction work,and hence, to reduce the construction cost and the period ofconstruction work.

Furthermore, the steel pipe ground reinforcement according to the above(1) is provided only with a recess portion in its outer peripheralsurface. Therefore, for example, after fabricating a steel pipe, thesteel pipe is only passed (as it is) between the rolls provided with aprotruded portion, to thereby make it possible to manufacture the steelpipe ground reinforcement. As a result, it is also possible to reducethe manufacturing cost more than the case of the conventional methodwithout lowering production efficiency.

Furthermore, it is possible to use the steel pipe ground reinforcementaccording to the above (1) similarly for reinforcement of a structuresuch as a concrete foundation of a building. Therefore, it is possibleto reinforce the structure at low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view showing an embodiment of a steel pipe groundreinforcement according to the present invention.

FIG. 2A is a diagram showing an embodiment of a steel pipe groundreinforcement according to the present invention.

FIG. 2B is a diagram showing a modification of the steel pipe groundreinforcement according to the present invention.

FIG. 2C is a diagram showing a modification of the steel pipe groundreinforcement according to the present invention.

FIG. 2D is a diagram showing a modification of the steel pipe groundreinforcement according to the present invention.

FIG. 2E is a diagram showing a modification of the steel pipe groundreinforcement according to the present invention.

FIG. 2F is a diagram showing a modification of the steel pipe groundreinforcement according to the present invention.

FIG. 2G is a diagram showing a modification of the steel pipe groundreinforcement according to the present invention.

FIG. 2H is a diagram showing a modification of the steel pipe groundreinforcement according to the present invention.

FIG. 2I is a diagram showing a modification of the steel pipe groundreinforcement according to the present invention.

FIG. 2J is a diagram showing a modification of the steel pipe groundreinforcement according to the present invention.

FIG. 2K is a diagram showing a modification of the steel pipe groundreinforcement according to the present invention.

FIG. 3A is a diagram showing a specific example of a recess portion of asteel pipe ground reinforcement according to the present invention.

FIG. 3B is a diagram showing another specific example of a recessportion of a steel pipe ground reinforcement according to the presentinvention.

FIG. 3C is a diagram showing another specific example of a recessportion of a steel pipe ground reinforcement according to the presentinvention.

FIG. 3D is a diagram showing another specific example of a recessportion of a steel pipe ground reinforcement according to the presentinvention.

FIG. 4 is a diagram showing a relationship between a width and a depthof a recess portion of a steel pipe ground reinforcement according tothe present invention.

FIG. 5 is a diagram showing a production line for a typical forge-weldedsteel pipe.

FIG. 6 is an example of a production line for forge-welded steel pipesthat manufactures a steel pipe ground reinforcement according to thepresent invention.

FIG. 7A is a conceptual diagram of rolls used for manufacturing a steelpipe according to the present invention.

FIG. 7B is a conceptual diagram of the rolls used for manufacturing asteel pipe according to the present invention.

FIG. 8 is another example of a production line for forge-welded steelpipes that manufactures a steel pipe ground reinforcement according tothe present invention.

FIG. 9 is a partial cross-sectional view of a forward end portion of asteel pipe ground reinforcement into which a drilling rod with a bit isinserted.

FIG. 10A is a diagram showing an evaluation method of a close contactforce in an example.

FIG. 10B is a diagram showing an evaluation method of a close contactforce in comparative examples.

FIG. 11 is a diagram comparing the effects in examples.

DESCRIPTION OF THE REFERENCE SYMBOLS

-   -   1: steel pipe    -   2: recess portion    -   3: through-hole    -   4: outer bit    -   5: steel pipe ground reinforcement

EMBODIMENTS OF THE INVENTION

Hereunder is a specific description of the present invention withreference to the drawings.

FIG. 1 schematically shows a steel pipe ground reinforcement 5 accordingto the present invention. The steel pipe ground reinforcement 5 includesa steel pipe 1 and recess portions 2 provided in an outer peripheralportion of the steel pipe 1. The recess portions 2 are circumferentiallyprovided there in a regularly spaced manner. With the recess portions 2,a frictional force between the steel pipe 1 and the ground, concrete, orthe like is increased.

In addition, over the whole peripheral surface of the steel pipe 1,there are arranged a plurality of through-holes 3 that communicatebetween the inside and outside of the steel pipe 1. A grouting materialinjected into the steel pipe 1 flows out to the outer surface of thesteel pipe through the through-holes 3. Some of the grouting material isfilled between the natural ground and the steel pipe 1 to fix thenatural ground with the steel pipe 1. Some of the grouting materialpermeates into the natural ground and becomes solidified, to therebyreinforce the natural ground. At this time, the recess portions 2 arebrought into a state of being buried in a layer of the solidifiedgrouting material. This securely integrates both. Therefore, even if aforce in the axial direction of the steel pipe 1 acts on the steel pipe1, engagement between the recess portions 2 and the grouting materiallayer produces hooking resistance, preventing the movement of the steelpipe 1.

As described above, with the steel pipe ground reinforcement 5 of thepresent embodiment, it is possible to improve the close contact betweenthe steel pipe 1 and the natural ground. This can fix the steel pipe 1with the natural ground more securely. In FIG. 1, reference numeral 4denotes an outer bit.

The manufacturing method of the steel pipe ground reinforcement 5requires only that, after fabrication of a steel pipe 1 on a steel pipeproduction line, recess portions 2 be provided in the surface of thesteel pipe 1 by means of a pressing device under hot or warm conditions.Therefore, productivity is substantially the same as that of an ordinarypipe fabrication step.

FIGS. 2A to 2K show specific examples of another shape of the recessportions 2.

In FIGS. 2A, 2B, and 2C, the steel pipe 1 has a plurality of recessportions 2A to 2C, respectively, in the circumferential direction. Therecess portions 2A to 2C are formed in a regularly spaced manner in theaxis direction. The steel pipe ground reinforcement 5 of FIG. 2A is anexample in which a plurality of (two in an opposing manner, in thefigure) recess portions 2A are provided on the same circumference of thesteel pipe 1. The steel pipe ground reinforcement 5 of FIG. 2B is one inwhich the recess portions 2 formed not by mill rolls but by areciprocal-type pressing apparatus capable of moving closer to orfurther away from the steel pipe 1A. The recess portion 2B hassubstantially the same depth on the circumference of the steel pipe 1.The steel pipe ground reinforcement 5 of FIG. 2C is an example in whicha plurality of recess portions 2C are provided in the circumferentialdirection of the steel pipe 1 and at least facing recess portions 2C ofthese do not exist on the same circumference.

With the facing recess portions 2C being arranged in a staggered mannerso as not to exist on the same circumference as is the case with thesteel pipe 1 of FIG. 2C, it is possible to improve the strength of thesteel pipe 1 at positions where the recess portions 2C are arrangedcompared with the case of the steel pipe 1 of FIG. 2A. The steel pipe 1shown in FIG. 2C is suitable for the case in which higher strength ofthe steel pipe ground reinforcement 5, especially at portions where therecess portion 2 are arranged, is required. In the example of thestaggered arrangement of the recess portions 2C, it is desirable thatthe recess portions 2C be formed so that their opposing portions do notoverlap with each other by the whole width.

FIGS. 2D to 2G are diagrams showing a steel pipe 1 in which recessportions 2D to 2G with long edges in directions diagonal to the axis ofthe steel pipe 1 are formed, respectively. FIG. 2H and FIG. 2I arediagrams showing a steel pipe 1 in which recess portions 2H, 2I withlong edges in a direction parallel to the axis of the steel pipe 1 areformed, respectively. FIG. 2J and FIG. 2K are diagrams showing a steelpipe 1 in which round spot-like (circular) recess portions 2J, 2K areformed, respectively. It is possible to freely select the shape of thespot-like recess portions 2J, 2K from an ellipse, a polygon, and thelike depending on easiness of their formation and the like. Furthermore,it is possible to freely select whether to arrange the recess portions2D to 2G on the same periphery, or whether to arrange them in astaggered manner.

Here, the shape of the recess portions 2D to 2G is limited only inheight. The only requirement is that space large enough to allow adrilling bit to pass through the inside of the steel pipe 1 is secured.

In the steel pipe ground reinforcement 5 of the present invention, therecess portions 2 are formed under hot or warm conditions as will bedescribed later. Therefore, it is possible to manufacture the steel pipe1 with ease even if it has a thickness of, for example, 2 mm or greater.Consequently, when a thick steel pipe ground reinforcement 5 ismanufactured and is driven into, for example, the ground while beingrotated a twisting force does not act on the steel pipe groundreinforcement 5 to be bent or to cause its forward end to be crushed. Inaddition, it is possible to easily manufacture a steel pipe with anouter diameter of 50 mm or greater that can be put to practical use as asteel pipe ground reinforcement 5.

In the case where the steel pipe ground reinforcement 5 according to thepresent invention is used for applications in which especially corrosionresistance is required, it is desirable that a surface of the steel pipe1 provided with the recess portions 2 be subjected to plating or resincoating, to thereby deliver favorable corrosion resistance.

As for the recess portion 2 of the steel pipe 1, its conceivablecross-sectional shape is basically a triangle or a rectangle, as shownin FIGS. 3A to 3D. A semicircle or a trapezoid may be regarded assubstantially a triangle. In any case, a depth H of the recess portion 2(which denotes a depth at its deepest point) requires 0.005×D (where Dis an outer diameter of the steel pipe) or greater in order to obtain africtional force between the peripheral surface of the steel pipe 1 andthe ground, concrete, or the like. However, an effect of improving africtional force is saturated above 0.2×D. Therefore, the depth H of therecess portion 2 is set to 0.005×D to 0.2×D. Furthermore, a width B ofthe recess portion 2 requires 0.015×D or greater to obtain thefrictional force. However, above 2×D, an effect of improving africtional force is small. Consequently, the depth H is required to beset to 2×D or less.

Furthermore, for optimizing the shape of the recess portion 2 under theabove preconditions, it is important to meet the following requirements.That is, when the cross-sectional shape of the recess portion 2 is atriangle, B/H=3 to 20. When the cross-sectional shape of the recessportion 2 is a rectangle, B/H=4 to 20. When the cross-sectional shape ofthe recess portion 2 is a semicircle or a trapezoid, B/H=3 to 20.

Hereunder is a description of how the above relationship of B/H isderived with reference to FIG. 4. As a precondition, a fracture mode forthe recess portion 2 is determined by either the shear strength of thesoil cement outside the recess portion 2, that is, at the base of thetriangle (the width B of the recess portion 2) in FIG. 4 or the bearingstrength of soil cement inside the recess portion 2. At this time, if afirst of the fracture modes obviously precedes a second fracture mode,it is conceived that the strength is decreased because the strength isdetermined by the first fracture mode. Therefore, to consider theoptimum shape of the recess portion 2, it is necessary to determine sucha shape to allow for simultaneous occurrence of the above two fracturemodes.

As a result, in the optimum shape of the recess portion 2, it isrequired that a bearing pressure P imparting a bearing strength and ashearing force S imparting a shear strength satisfy a conditionalequation for equilibrium expressed as equation (1) as follows:

S=Pcosθ  (1)

where θ is an angle formed by the surface of the steel pipe 1 and theentry side surface of the recess portion 2.

Here the shearing force S is defined by (area on which the shearingforce acts)×(shearing force). Therefore, the shearing force S isformulated as an equation (2) shown below. Here, it is assumed that therecess portions 2 are arranged over the whole periphery of the steelpipe 1. A shear area is expressed by a product of a peripheral length 1Dof the steel pipe 1 and a width B of the recess portion 2 (base portionof the triangle) as follows:

S=tτ·B·π·D  (2).

On the other hand, the bearing pressure P is a bearing stress multipliedby an area on which the bearing stress acts, which is formulated as anequation (3) as follows:

P=H·σb·cosθ·π·D  (3)

where τ is a shear stress, D is an outer diameter of the steel pipe, andσb is a bearing pressure (bearing stress, dimension of force/area).

Substitution of the equations (2), (3) into the equation (1) yieldsequations (4), and hence (4′), as follows:

τ·B=(H·σb·cosθ)cosθ  (4)

∴B/H=σb·cos²θ/τ  (4′).

The equation (4′) is a modification of the conditional equation of forceequilibrium when the optimum shape is provided to the recess portion 2.Here, the equation (4′) is solved for the case where an angle (θ) formedby a side surface of the recess portion 2, that is, an oblique surfaceof the triangle in FIG. 4 and a surface of the steel pipe 1 is 45degrees (hereinafter, referred to as a triangular shape) and 90 degrees(hereinafter, referred to as a rectangular shape).

Letting 0=90° (the recess portion 2 have a rectangular shape),

B/H=σb/τ  (5).

For example, substitution of the soil cement's bearing strength σb=1N/mm² and its shear strength τ=0.1 N/mm² into the equation (5) yieldsB/H=10 (the width of recess portion 2 is ten times its height). As aresult, the recess portion 2 has a shape of a rectangle with a length of10H and a height of H.

On the other hand, if the final shape of the recess portion 2 is atriangular shape and also the triangle is isosceles, then B, H, and θsatisfy a relational expression (6) as follows:

tan θ=2·H/B  (6).

Substituting this into the equation (4′) yields

2/(sin θ·cosθ)=σb/τ  (7).

Substitution of the soil cement's bearing strength σb=1 N/mm² and itsshear strength τ=0.1 N/mm² into this equation (7) yields

sin θ·cos θ=⅕  (8)

sin 2θ=⅖=0.4  (8′).

∴θ=11.8

Letting the relationship between the soil cement's (concrete's) bearingstrength σb and its shear strength τ be

1/20≦Σ/σb≦ 2/9 (typically, τ/σb=approximately 1/10),

(a) if the recess portion 2 has a shape of a triangle, the relationshipbetween the width B and the depth H of the recess portion 2 is obtainedfrom the equation (5) as:

4.5≦B/H≦20.0

(b) if the recess portion 2 has a shape of a triangle, a proper range of0 is obtained from the equation (7) as:

5.8≦θ≦31.4

At this time, the relationship between the width B and the depth H ofthe recess portion 2 is obtained from the equation (6) as:

3.3≦B/H≦19.8

Here, in the case of the recess portions 2 with a shape diagonal orparallel to the axis direction of the steel pipe 1 or the spot-likerecess portions 2 as shown in FIGS. 2D to 2K, the aforementionedequations may be applied also to the A-A cross-section of FIG. 2D, theH-H cross-section of FIG. 2H, and the C-C cross-section of FIG. 2J.

As described above, in the present invention, B/H is prescribed asfollows:

(1) If the cross-section of the recess portion 2 has a triangular shape,B/H=3 to 20

(2) If the cross-section of the recess portion 2 has a rectangularshape, B/H=4 to 20

(3) If the cross-section of the recess portion 2 has a semicircular ortrapezoidal shape, B/H=3 to 20.

Next is a description of a manufacturing method of the steel pipe groundreinforcement 5 according to the present invention.

In the present invention, any of the following steps of a), b), c), andd) may be used. The present invention will be described for the case ofa production line for forge-welded steel pipes by way of representativeexample.

a) After being welded by electric resistance welding on a steel pipeproduction line for electric resistance welding, a steel pipe is heatedand its surface is pressed by a pressing device.

b) After a steel pipe is welded on a steel pipe production line for hotor warm welding, its surface is pressed by a pressing device.

c) After a steel pipe is butt-welded on a steel pipe production line forforge-welding, its surface is pressed by a pressing device.

d) After a tube is fabricated on a seamless steel pipe production line,its surface is pressed by a pressing device.

FIG. 5 is a diagram showing a typical production line for forge-weldedpipes.

Steel belts 10 that are cut into a desired width are formed in acircular cross-section by rolls 21. After that, both corresponding endsthereof are heated to high temperatures, pressed to each other, andbutt-welded by rolls 22 into a pipe. By narrowing the butt-welded pipedown with following rolls 23 to 34, the pipe is reduced in diameter to apredetermined size. The pipe is then cut by a cutter 38 intopredetermined lengths, and their shapes are adjusted by following rolls35 to 37. Thus, forge-welded pipes 11 (steel pipes 1) are manufactured.

FIG. 6 is an embodiment of a production line for forge-welded pipes.

A difference from a conventional production line lies in that only thefinal rolls 34 of the reduction rolls before the cutter 38 are modified.As shown in FIGS. 7A, 7B, in the roll 34, one or more protruded portionsα are provided on the peripheral surface of the roll 34 in the roll axisdirection. The protruded portion a functions as a pressing device. Theroll 34 provided with the protruded portions α is used on one or both ofthe upper and lower sides. FIGS. 6, 7A, and 7B show a set of two rolls34 a, 34 b on the upper and lower sides, respectively. However, a set ofmore than three rolls may be provided. By the rolls 34 with suchprotruded portions α, a pressure is applied to a forge-welded pipe 11 athigh temperatures (approximately 1200 to 1300° C.). Therefore, inportions of the forge-welded pipe 11 brought into contact with theprotruded portions α, recess portions 2 are formed with ease. Inaddition, compared with cold working, a shape of the recess portion 2 isformed in accordance with the shape of the protruded portion a of theroll 34. Consequently, it is possible to obtain recess portions 2 withan acuter angle. After that, the forge-welded pipe 11 is cut intopredetermined lengths and sized. Thus, a steel pipe ground reinforcement5 with recess portions 11 a of the present invention is completed.

Here, to modify the recess portions 2 on the forge-welded pipe 11 intheir height, width, or pitch, the protruded portions a of the roll 34may be modified in their shape or pitch. Furthermore, in order to formrecess portions 2 on the forge-welded pipe 11 at the same location,protruded portions a may be provided on both of the upper and lowerrolls 34 a, 34 b, and the positions of protruded portions a of the upperand lower rolls 34 a, 34 b may be matched at an initial stage. In thiscondition, the upper and lower rolls 34 a, 34 b may be coupled via, forexample, a single drive source and a single universal joint or the like,to thereby synchronously drive the upper and lower rolls 34 a, 34 b

It is desirable that the protruded portion a formed on the roll 34 beshaped so as to be highest at its central portion and be lower as it iscloser to the edge portions of the roll 34, as shown in FIG. 7B. Thereason is this. The central portion and edge portion of the roll 34 havedifferent peripheral velocities. The edge portion, which has a largerdiameter, has a higher peripheral velocity. Accordingly, the roll 34rotates faster than the passing pipe, applying an unnecessary force onthe forge-welded pipe 11. As a result, excessive deformation ordistortion is produced in the forge-welded pipe 11.

FIG. 8 shows another example of a production line for forge-weldedpipes.

This production line is an example in which a dedicated pressuringapparatus (pressing device) 39 for applying pressure to the forge-weldedpipe 11 (steel pipe 1) is provided between the reduction rolls 34 andthe cutter 38. As the pressurizing apparatus 39, the aforementioned roll34 with protruded portions a may be used. Alternatively, one of a typethat applies pressure to the forge-welded pipe 11 from top and bottommay be used. It is desirable that the pressurizing apparatus 39 have amechanism capable of moving forward and backward with respect to theforge-welded pipe 11 or capable of moving forward and backward withrespect to the moving direction of the forge-welded pipe 11.

With the pressurizing apparatus 39 being capable of moving closer to andaway from the forge-welded pipe 11, it is possible to form the recessportion 2 at an optional position of the forge-welded pipe 11. Even whenthe pitch between the recess portions 2 is to be modified, the rolls 34need not be replaced. Furthermore, with this function, it is possiblefor the recess portions 2 to be controlled by control portions so as notto be placed at cut positions of the forge-welded pipe 11 that arepreviously recognized by the control portion. When the recess portions 2coincide with the end portions of the forge-welded pipes 11, differentforge-welded pipes 11 have end faces different in diameter and shape.This makes it difficult, for example, to connect the forge-welded pipes11 to each other.

Furthermore, with the pressurizing apparatus 39 being capable of movingin the moving direction of the forge-welded pipe 11, it is possible tomove the reduced-diameter formation apparatus in synchronization with amovement of the forge-welded pipe 11. This makes it possible tounboundedly form of the shape of the recess portion 2 without excessivedistortion of the forge-welded pipe 11 produced by a difference inperipheral velocity between the central portion and edge portion of theroll 34 as described above.

While description has been for the dedicated apparatus, the functions ofthe dedicated apparatus may be provided to rolls 34, which are existingfinal reduction rolls with protruded portions α.

As described above, the pipe fabrication method may be any of the pipefabrication method by electric resistance welding, the pipe fabricationmethod in which pipes are hot- or cold-welded, the pipe fabricationmethod by forge-welding, and the seamless pipe fabrication method. Thesurface of the fabricated pipe may be pressed by a pressing device underwarm or hot conditions that are brought about by heating or the likeduring or after the pipe fabrication. This enables online manufacture ofa steel pipe 1 with recess portions 2.

The steel pipe 1 manufactured by any of the manufacturing methods hasthe recess portions 2 formed under hot conditions. Therefore, it ispossible to easily manufacture the steel pipe 1 even if the steel pipe 1has a thickness of 2 mm or greater. For example, when the steel pipe 1is rotated to be driven into the ground as a steel pipe pile, it doesnot occur that a twisting force acts on the steel pipe 1 to cause thesteel pipe 1 to be bent or its forward end to be crushed, because thesteel pipe 1 is thick. Furthermore, it is also possible to easilymanufacture a pipe with an outer diameter of 50 mm or greater that canbe put to practical use as a steel pipe ground reinforcement 5. Inaddition, its production efficiency is the same as that when typicalforge-welded steel pipes are manufactured.

With a steel pipe being manufactured by dedicated roll(s) provided withprotrusion(s) on a production line for typical steel pipes by the steelpipe manufacturing method as described above, it is possible tocontinuously provide recess portions 2 simultaneously with themanufacture of the steel pipe. Furthermore, with modification in shapeof the protruded portion(s) α of the dedicated roll(s) 34, it ispossible to provide recess portions 2 with optional shape, pitch, andarrangement. In addition, this eliminates the necessity of working inanother step, making it possible to provide a steel pipe 1 with recessportions 2 at a very low cost.

In the steel pipe ground reinforcement 5 of the present invention, notexternally-protruded shapes but internally-protruded shapes (that is,recess portions 2) are provided in the surface of the steel pipe 1.Thereby, when the steel pipe 1 is driven, the recess portions 2 do notfunction as obstacles. Furthermore, it is possible to manufacture asteel pipe ground reinforcement 5 with large recess portions 2 capableof securing sufficient close contact, at a low cost without reducingproductivity

Then, in the steel pipe 1 provided with the recess portions 2, aplurality of through-holes 3 are bored. The through-holes 3 may beprovided in the recess portions 2 on the periphery of the steel pipe 1or in a smooth portion outside the recess portions 2. Alternatively,through-holes 3 may be provided in both. The diameter and arrangement ofthrough-holes 3 are required only to allow the grouting material tospread over the whole length of the steel pipe 1, and hence may beoptionally determined according to the characteristic and condition ofthe grouting material and to the condition of the ground.

FIG. 9 is a diagram showing a positional relationship among drillingbits 4, 7 and the steel pipe ground reinforcement 5. The outer bit 4,while rotating by the motive force transmitted from the rod 6 and theinner bit 7, drills the ground and the like ahead. Behind the outer bit4, the steel pipe ground reinforcement 5 of the present invention isarranged. Therefore, the outer diameter of the steel pipe groundreinforcement 5 is required only to be smaller than the outer diameterof the outer bit 4.

The rod 6 and the inner bit 7 extend through the inside of the steelpipe ground reinforcement 5. Therefore, the minimum inner diameter ofthe steel pipe 1 is required to be larger than the maximum outerdiameter of the inner bit 7. So long as the above conditions are met,the recess portion 2 on the periphery of the steel pipe 1 can be madedeeper.

To use the steel pipe ground reinforcement 5, the drilling rod 6 withthe inner bit 7 attached to its forward end portion is inserted throughthe steel pipe 1, as shown in FIG. 9. In this condition, the rearwardend portions of the drilling rod 6 and the steel pipe 1 are connected toa rock drill (not shown in the figure) such that the inner bit 7 of theforward end portion is set to protrude past the outer bit 4 of the steelpipe 1. Then, boring is performed while strike, rotation, and thrust arebeing applied to the drilling rod 6 and the steel pipe 1 from the rockdrill. During the boring, water or compressed air is supplied from therock drill, and is discharged from the forward end portion of the outerbit 4. Most of the cuttings produced by the boring pass through theinside of the steel pipe 1 and are discharged. However, part of thempass over the outside of the steel pipe 1 and are discharged backwardly.

After completion of boring a hole with a predetermined depth and thesteel pipe 1 is buried into the natural ground, the drilling rod 6together with the inner bit 7 is pulled out backwardly from the steelpipe 1. After that, an injection apparatus (not shown in the figure) isattached to the rearward end portion of the steel pipe 1, and a groutingmaterial is injected into the steel pipe 1. The grouting material fillsthe steel pipe 1, and flows to the outside through the multitude ofthrough-holes 3 provided in the steel pipe 1. Then, while flowing alongthe outer surface of the steel pipe 1, the grouting material permeatesinto the natural ground and becomes solidified. Thereby, the naturalground is reinforced.

The steel pipe 1 has the recess portions 2 formed in its outerperipheral portion. Therefore, the recess portions 2 are brought into astate of being buried in a layer of the solidified grouting material.This securely integrates both. As a result, even if a force in the axisdirection acts on the steel pipe 1, engagement between the recessportions 2 and the grouting material layer produces hooking resistance,preventing movement of the steel pipe 1. Thus, the steel pipe 1 issecurely fixed in the natural ground. The recess portions 2 have apredetermined cross-sectional shape. Therefore, it is possible toimprove both hooking resistance for preventing displacement and fluidityof grouting material and cuttings.

The recess portions 2 are typically formed by milling rolls. Therefore,their cross-sectional shape is a smooth shape without an edge or acorner. Therefore, the cuttings and the grouting material smoothly flow,preventing the partial formation of clogging or a gap. As a result, notonly a discharge state of the cuttings is favorable, but also closecontact between the grouting material and the steel pipe 1 improves.Thereby, it is possible to achieve excellent ground enforcement. In theabove description, a combination of the ring-like outer bit 4 affixed tothe forward end portion of the steel pipe 1 and the inner bit 7 attachedto the forward end portion of the drilling rod 6 is adopted as a bit.However, an expandable bit capable of expanding and shrinking itsdiameter may be used. During boring, a hole of the bit may be bored sothat its diameter is larger than the outer diameter of the steel pipe 1.At the end of boring, the diameter of the expandable bit may be shrunkso that it is smaller than the inner diameter of the steel pipe 1, andthe bit may be pulled out backwardly. When the expandable bit is used,the ring bit (outer bit) 4 need not be fixed to the forward end portionof the steel pipe 1.

EXAMPLES

Next is a description of a comparison of close contact forces on thefollowing levels. The number of the levels is three as shown in Table 1.Size: 76.3 mmφ×3.2 mm t×6 m L, Standard: JIS G 3444 STK

TABLE 1 Comparative Example 1 Straight pipe Typical straight pipeComparative Steel pipe with Externally spiral deposit-welded steel pipeExample 2 protrusions (equivalent to Japanese Unexamined PatentApplication, First Publication No. 2006-022501) <Deposit dimension>height: 5 mm × width: 5 mm × lead: 300 mm, lead angle: 30 degreesPresent Steel pipe with Steel pipe provided with recesses Examplerecesses <Step shape> Step shape: triangular step portions provided incircumferential direction, equally spaced in pipe axis direction (spacebetween steps: 200 mm) depth: 8 mm × width: 40 mm

In the evaluation method of the close contact forces, the steel pipeground reinforcement 5 is buried in a soil cement 100 and a load isapplied thereon by an upper portion 101, as shown in FIGS. 10A, 10B.Thereby, a maximum load was measured (Degree of close contact wasmeasured at a maximum load). FIG. 10A is a diagram schematically showingan evaluation method when the steel pipe ground reinforcement 5 of thepresent invention is buried. FIG. 10B is a diagram schematically showingan evaluation method when a steel pipe 102 provided with protrudedportions 103 is buried as a comparative example 2.

As the soil cement 100, a mixture of soil and solidification materialwas used. Two types of soil were used: cohesive soil and sandy soil. Thecohesive soil had a particle size of 0.001 to 0.005 mm. The sandy soilhad a particle size of 0.074 to 2.000 mm. As a result, it has beenrecognized that the present invention has a heavier push-out load, thatis, a greater close contact force than Comparative Examples, as shown inFIG. 11.

The manufacturing cost of the steel pipe ground reinforcement formedwith the recess portions of the present invention is substantially thesame as the Comparative Example 1. On the other hand, for the steel pipewith protrusions of Comparative Example 2, a deposit welding cost forforming the protruded portions is added to a pipe fabrication cost. Thisresults in a higher cost. Therefore, it is understood that the presentinvention is excellent also in cost.

INDUSTRIAL APPLICABILITY

As is clear from the above description, the steel pipe groundreinforcement according to the present invention is one in which recessportions are formed in an outer peripheral surface of a conventionalsteel pipe, and is capable of reinforcing the ground in a tunnelconstruction and the like or capable of reinforcing a structure such asa concrete foundation at a low cost with efficiency.

1. A steel pipe ground reinforcement that is driven into a ground and injects a grouting material into the ground, the steel pipe ground reinforcement comprises: a recess portion and a smooth portion that are arranged on an outer peripheral surface thereof; and a plurality of through-holes that are arranged in the recess portion or the smooth portion that communicates between an inside and an outside of the steel pipe ground reinforcement.
 2. The steel pipe ground reinforcement according to claim 1, wherein the recess portion has a cross-sectional shape with a depth of the recess portion of 0.005 D to 0.2 D and a width of the recess portion of 0.015 D to 2D where D is an outer diameter of the steel pipe, and wherein the recess portion has a triangular shape in cross-section, and B/H=3 to 20 where B is the width of the recess portion and H is the depth of the recess portion.
 3. The steel pipe ground reinforcement according to claim 1, wherein the recess portion has a cross-sectional shape with a depth of the recess portion of 0.005 D to 0.2 D and a width of the recess portion of 0.015 D to 2D where D is an outer diameter of the steel pipe, and wherein the recess portion has a rectangular shape in cross-section, and B/H=4 to 20 where B is the width of the recess portion and H is the depth of the recess portion.
 4. The steel pipe ground reinforcement according to claim 1, wherein the recess portion has a cross-sectional shape with a depth of the recess portion of 0.005 D to 0.2 D and a width of the recess portion of 0.015 D to 2D where D is an outer diameter of the steel pipe, and wherein the recess portion has a semicircular or trapezoidal shape in cross-section, and B/H=3 to 20 where B is the width of the recess portion and H is the depth of the recess portion.
 5. The steel pipe ground reinforcement according to claim 1, wherein a plurality of the recess portions are provided on a same periphery of the steel pipe.
 6. The steel pipe ground reinforcement according to claim 1, wherein a plurality of the recess portions are provided in a circumferential direction of the steel pipe, and wherein at least the recess portions that face each other are provided so as to avoid being on a same periphery of the steel pipe.
 7. The steel pipe ground reinforcement according to claim 1, wherein a plurality of the recess portions are provided diagonally with respect to an axis of the steel pipe.
 8. The steel pipe ground reinforcement according to claim 1, wherein a plurality of the recess portions are provided in parallel with respect to an axis of the steel pipe.
 9. The steel pipe ground reinforcement according to claim 1, wherein a plurality of the recess portions are provided in a circular shape when seen from front.
 10. The steel pipe ground reinforcement according to claim 1, wherein plating or resin coating is provided on the surface of the steel pipe.
 11. A method of reinforcing a ground, comprising: when reinforcing a ground, driving the steel pipe ground reinforcement according to claim 1 while drilling the ground; and after driving of the steel pipe ground reinforcement, injecting a grouting material into an inside of the steel pipe ground reinforcement to thereby inject the grouting material into an outside of the steel pipe ground reinforcement through the plurality of through-holes.
 12. The method of reinforcing a ground according to claim 11, wherein a minimum inner diameter of the steel pipe ground reinforcement is larger than an outer diameter of an inner bit that is used when the ground is drilled.
 13. The method of reinforcing a ground according to claim 11, wherein a maximum outer diameter of the steel pipe ground reinforcement is smaller than an outer diameter of an outer bit that is used when the ground is drilled.
 14. A method of reinforcing a structure including concrete, comprising: when reinforcing a structure, driving the steel pipe ground reinforcement according to claim 1 while drilling the structure; and after driving of the steel pipe ground reinforcement, injecting a grouting material into an inside of the steel pipe ground reinforcement to thereby inject the grouting material into an outside of the steel pipe ground reinforcement through the plurality of through-holes. 